Doc for Content Template:
https://docs.generatepress.com/article/block-element-content-template/
This can be applied to a single post or a archive page.
Doc for Loop Template:
https://docs.generatepress.com/article/block-element-loop-template/
This can be applied to only a archive page.
In either ( all ) elements you can set the Display Rule > Location for where you want it applied.
For a single post in a specific category use: Post Category -> the category term
For a archive you can use Post Category Archive -> and either the category term(s) or All Categories